1. Field of the Invention
This invention is directed to a slitter-sealer apparatus for slitting multiple layers of thermoplastic polymer film and sealing the edges of adjacent layers together for bag-making, bag-sealing and similar operations with thermoplastic synthetic polymer composition film.
2. Brief Description of the Prior Art
Thermoplastic synthetic polymer composition film is folded, cut, edge-sealed and similarly processed for the automatic making of those receptacles commonly called "plastic bags." Such bags are used for the packing, storing and handling of a wide variety of products, with the food processing industry consuming a large amount of film and a large number of bags. In making such items, the film is produced and is wound on a supply roll in double thickness, with the edges already sealed or continuous so that the supply roll carries a wide tube. When it is desired to make two bags per width of tube, the double layer of flim is advanced through a slitter which slits the multiple layers and, at the same time, seals the adjacent layers together to form a pair of narrower tubes. The slitter is a sharp bifurcated knife blade, and sealing is accomplished by heating the slitter. When operating at the normal high film speed, the slitter blade must be heated to a quite high temperature in order to raise the thermoplastic film to sealing temperature. One of the problems is that, with such a high temperature, the film is often locally overheated, causing crystallization which weakens the material at the joint. Also, the overheating often causes the film to be so soft and therefore weak immediately after passing the slitter that the forces occurring during rapid film travel cause separation or at least weakening of the joint. Thus, failure most often occurs at the sealed joint. There is need in the art to produce an improved polymer film slitter-sealer apparatus so that high-speed splitting and sealing can be accomplished with a reliable, strong seal joint.